1. Technical Field
The present disclosure relates to a search method, a search device, and a search system, in which a similarity search is performed while keeping content secret by encryption.
2. Description of the Related Art
In recent years, there are systems where a user can measure blood pressure or the like, for example, in the home, and transmit information of the measurement results from a user terminal to a server. This information is analyzed at the server, and the user is provided with dietary advice and the like. This system is capable of providing the user with useful advice by performing this analysis referencing not only past information of the user him/herself, but other similar cases as well. Searching for similar cases (similarly search) at the server preferably is performed with user information and the like kept secret through encryption, from the perspective of protection of privacy. International Publication No. 2014/185450 discloses technology for a verification system where data to be authenticated and authentication data are verified while left encrypted, by using additive homomorphic encryption, thereby keeping the data secret to the server.
Also referenced in the present specification are Allison Bishop et al, “Function-Hiding Inner Product Encryption”, Advances in Cryptology—ASIACRYPT 2015, published by Springer Berlin Heidelberg (URL: https://eprint.iacr.org/2015/672.pdf), hereinafter referred to simply as “BISHOP”, and Emily Shen et al., “Predicate Privacy in Encryption Systems”, Theory of Cryptography, published by Springer Berlin Heidelberg (URL: https://eprint.iacr.org/2008/536.pdf), hereinafter referred to simply as “SHEN”.
However, conventional similarity searching required the user terminal to encrypt user information and transmit to the server, and the user terminal to verify reference information that is the results of the server having performed the search with the information left encrypted, is if the amount of reference information is great, the processing load on the user terminal is great, and the amount of communication increases.